Alkylated diphenylamines are well-known anti-oxidants such as for use as additive components in lubricating oil compositions (or lubricants) for lubricating the crankcase of spark-ignited or compression-ignited internal combustion engines. The art describes making them by catalytically alkylating diphenylamine by means of an alkene (or alkylene) alkylating agent. Among the alkylating agents described in the art there are mentioned oligomers of propene, also referred to as propylene.
U.S. Pat. No. 5,214,211 mentions use of propylene oligomers to alkylate diphenylamine.
EP-A-0416 914 describes p,p′-dialkyldiphenylamine with branched alkyl groups having 12 or 15 carbon atoms, derived from oligomers of propylene.
U.S. Pat. No. 6,315,925 A describes nonylated diphenylamines using tripropylene, a C9 olefin, as the nonylating agent. Nonylated diphenylamines are used commercially as anti-oxidants in crankcase lubricants; examples include Irganox® L57 and Naugalube® 640.
US 2004/0211113 A1 describes producing alkylated diphenylamines by alkylating a diphenylamine with a mixture of oligomers of propylene, but does not identify the oligomers that may be used.
US 2006/0276677 A1 describes alkylating diphenylamine with an alkylating agent in the form of an alkylene, or mixture of isomeric olefins, having 4 to 28 carbon atoms. The use of propylene tetramer, a C12 olefin, as alkylating agent is specifically exemplified.
Gatto et al, in a paper entitled “Redesigning alkylated diphenylamine antioxidants for modern lubricants” and published in Lubrication Science 2007; 19: 25-40 report tests on C9 and propylene tetramer C12 alkylated diphenylamines and conclude that data were presented showing that high molecular weight diphenylamines are less effective on an equal weight basis than the other structures examined.
A problem in the art is to provide alkylated diphenylamines, derived from propene oligomers, that have surprisingly advantageous properties as lubricant additives particularly in respect of piston deposits and engine sludge, as well as having satisfactory effectiveness as lubricant anti-oxidants. The art makes no mention of alkylated diphenylamines having piston deposit reduction properties.